In vertebrate animals, the heart is a hollow muscular organ having four pumping chambers: the left and right atria and the left and right ventricles, each provided with its own one-way valve. The natural heart valves are identified as the aortic, mitral (or bicuspid), tricuspid and pulmonary, and are each mounted in an annulus comprising dense fibrous rings attached either directly or indirectly to the atrial and ventricular muscle fibers. Each annulus defines a flow orifice.
Heart valve disease is a widespread condition in which one or more of the valves of the heart fails to function properly. Diseased heart valves may be categorized as either stenotic, wherein the valve does not open sufficiently to allow adequate forward flow of blood through the valve, and/or incompetent, wherein the valve does not close completely, causing excessive backward flow of blood through the valve when the valve is closed. Valve disease can be severely debilitating and even fatal if left untreated.
Various surgical techniques may be used to repair a diseased or damaged valve. In a valve replacement operation, the damaged leaflets are excised and the annulus sculpted to receive a replacement valve. Another less drastic method for treating defective valves is through repair or reconstruction, which is typically used on minimally calcified valves. One repair technique that has been shown to be effective in treating incompetence is annuloplasty, in which the deformed valve annulus is reshaped by attaching a prosthetic annuloplasty repair segment or ring to the valve annulus. The annuloplasty ring is designed to support the functional changes that occur during the cardiac cycle: maintaining coaptation and valve integrity to prevent reverse flow while permitting good hemodynamics during forward flow.
The annuloplasty ring typically comprises an inner substrate of a metal such as rods or bands of stainless steel or titanium, or a flexible material such as silicone rubber or Dacron cordage, covered with a biocompatible fabric or cloth to allow the ring to be sutured to the fibrous annulus tissue. Annuloplasty rings may be stiff or flexible, split or continuous, and may have a variety of shapes, including circular, D-shaped, C-shaped, or kidney-shaped. Examples are seen in U.S. Pat. Nos. 5,041,130, 5,104,407, 5,201,880, 5,258,021, 5,607,471 and, 6,187,040 B1. Most annuloplasty rings are formed in a plane, with some D-shaped mitral rings being bowed along their straight side to conform to the shape of the annulus at that location. Whether totally flexible, rigid, or semi-rigid, annuloplasty rings have been associated with a 10% to 15% ring dehiscence incidence at 10 years, thus requiring a reoperation. The present invention is intended to reduce this complication.
For the purposes of anatomic orientation, please refer to FIG. 1, which is a schematic representation of the AV junctions within the heart and the body in the left anterior oblique projection. The body is viewed in the upright position and has 3 orthogonal axes: superior-inferior, posterior-anterior, and right-left. Traditional nomenclature for the AV junctions derives from a surgically distorted view, placing the valvular rings in a single horizontal plane with antero-posterior and right-left lateral coordinates. The descriptive terms used, however, are anatomically inaccurate. An accurate account of the coordinates of the valvular orifices is provided by the simple expedient of relating appropriately the view obtained in left anterior oblique projection to the supero-inferior and antero-posterior coordinates of the body.
FIG. 2 is a cutaway view of the heart from the front, or anterior, perspective, with most of the primary structures marked. As is well known, the pathway of blood in the heart is from the right atrium to the right ventricle through the tricuspid valve, to and from the lungs, and from the left atrium to the left ventricle through the mitral valve. The present application has particular relevance to the repair of the tricuspid valve, which regulates blood flow between the right atrium and right ventricle, although certain aspects may apply to repair of other of the heart valves. The tricuspid and mitral valves together define the atrioventricular (AV) junctions.
As seen in FIG. 2, four structures embedded in the wall of the heart conduct impulses through the cardiac muscle to cause first the atria then the ventricles to contract. These structures are the sinoatrial node (SA node), the atrioventricular node (AV node), the bundle of His, and the Purkinje fibers. On the rear wall of the right atrium is a barely visible knot of tissue known as the sinoatrial, or SA node. This tiny area is the control of the heart's pacemaker mechanism. Impulse conduction normally starts in the SA node. It generates a brief electrical impulse of low intensity approximately 72 times every minute in a resting adult. From this point the impulse spreads out over the sheets of tissue that make up the two atria, exciting the muscle fibers as it does so. This causes contraction of the two atria and thereby thrusts the blood into the empty ventricles. The impulse quickly reaches another small specialized knot of tissue known as the atrioventricular, or AV node, located between the atria and the ventricles. This node delays the impulse for about 0.07 seconds, which is exactly enough time to allow the atria to complete their contractions. When the impulses reach the AV node, they are relayed by way of the several bundles of His and Purkinje fibers to the ventricles, causing them to contract. As those of skill in the art are aware, the integrity and proper functioning of the conductive system of the heart is critical for good health.
FIG. 3 is a schematic view of the tricuspid valve orifice seen from its inflow side (from the right atrium), with the peripheral landmarks labeled as: antero septal commissure, anterior leaflet, posterior commissure, antero posterior leaflet, postero septal commissure, and septal leaflet. Contrary to traditional orientation nomenclature, the tricuspid valve is nearly vertical, as reflected by these sector markings. From the same viewpoint, the tricuspid valve 20 is shown surgically exposed in FIG. 4 with an annulus 22 and three leaflets 24a, 24b, 24c extending inward into the flow orifice. Chordae tendineae 26 connect the leaflets to papillary muscles located in the RV to control the movement of the leaflets. The tricuspid annulus 22 is an ovoid-shaped fibrous ring at the base of the valve that is less prominent than the mitral annulus, but larger in circumference.
Reflecting their true anatomic location, the three leaflets in FIG. 4 are identified as septal 24a, anterior 24b, and posterior (or “mural”) 24c. The leaflets join together over three prominent zones of apposition, and the peripheral intersections of these zones are usually described as commissures 28. The leaflets 24 are tethered at the commissures 28 by the fan-shaped chordae tendineae 26 arising from prominent papillary muscles originating in the right ventricle. The septal leaflet 24a is the site of attachment to the fibrous trigone, the fibrous “skeletal” structure within the heart. The anterior leaflet 24b, largest of the 3 leaflets, often has notches. The posterior leaflet 24c, smallest of the 3 leaflets, usually is scalloped.
The ostium 30 of the right coronary sinus opens into the right atrium, and the tendon of Todaro 32 extends adjacent thereto. The AV node 34 and the beginning of the bundle of His 36 are located in the supero-septal region of the tricuspid valve circumference. The AV node 34 is situated directly on the right atrial side of the central fibrous body in the muscular portion of the AV septum, just superior and anterior to the ostium 30 of the coronary sinus 30. Measuring approximately 1.0 mm×3.0 mm×6.0 mm, the node is flat and oval. The AV node 34 is located at the apex of the triangle of Koch 38, which is formed by the tricuspid annulus 22, the ostium 30 of the coronary sinus, and the tendon of Todaro 32. The AV node 34 continues on to the bundle of His 36, typically via a course inferior to the commissure 28 between the septal 24a and anterior 24b leaflets of the tricuspid valve; however, the precise course of the bundle of His 36 in the vicinity of the tricuspid valve may vary. Moreover, the location of the bundle of His 36 may not be readily apparent from a resected view of the right atrium because it lies beneath the annulus tissue.
The triangle of Koch 38 and tendon of Todaro 32 provide anatomic landmarks during tricuspid valve repair procedures. A major factor to consider during surgery is the proximity of the conduction system (AV node 34 and bundle of His 36) to the septal leaflet 24a. Of course, surgeons must avoid placing sutures too close to or within the AV node 34. C-shaped rings are good choices for tricuspid valve repairs because they allow surgeons to position the break in the ring adjacent the AV node 34, thus avoiding the need for suturing at that location.
A rigid C-shaped ring of the prior art is the Carpentier-Edwards Classic® Tricuspid Annuloplasty Ring sold by Edwards Lifesciences Corporation of Irvine, Calif., which is seen in FIGS. 5A and 5B. Although not shown, the planar ring 40 has an inner titanium core (not shown) covered by a layer of silicone and fabric. Rings for sizes 26 mm through 36 mm in 2 mm increments have outside diameters (OD) between 31.2-41.2 mm, and inside diameters (ID) between 24.3-34.3 mm. These diameters are taken along the “diametric” line spanning the greatest length across the ring because that is the conventional sizing parameter. A gap G between free ends 42a, 42b in each provides the discontinuity to avoid attachment over the AV node 34. The gap G for the various sizes ranges between about 5-8 mm, or between about 19%-22% of the labeled size. As seen in the implanted view of FIG. 6, the gap G is sized just larger than the AV node 34. Despite this clearance, some surgeons are uncomfortable passing sutures so close to the conductive AV node 34, particularly considering the additional concern of the bundle of His 36.
A flexible C-shaped tricuspid band is sold under the name Sovering™ by Sorin Biomedica Cardio S.p.A. of Via Crescentino, Italy. The Sovering™ band is made with a radiopaque silicone core covered with a knitted polyester (PET) fabric so as to be totally flexible. Bands for sizes 28 mm through 36 mm in 2 mm increments have outside diameters (OD) between 33.8-41.8 mm, and inside diameters (ID) between 27.8-35.8 mm. As with other tricuspid rings, a gap between the free ends provides a discontinuity to avoid attachment over the AV node. The nominal gap for the various sizes ranges of the Sovering™ band ranges between about 18-24 mm, or between about 60%-70% of the labeled size. Although this nominal gap helps avoid passing sutures close to the conductive AV node 34 and bundle of His 36, the band is designed to be attached at the commissures on either side of the septal leaflet and thus no support is provided on the septal side.
Despite numerous designs presently available or proposed in the past, there is a need for a prosthetic tricuspid ring that better harmonizes with the physiologic features of the tricuspid annulus, and in particular for a prosthetic tricuspid ring that better fits the contours of the tricuspid annulus and presents selective flexibility to reduce the stress in the attachment sutures, while at the same time reduces the risk of inadvertently passing a suture through the critical physiologic structures within the heart that conduct impulses.